Current limit for a power tool powered by different power supplies

A power tool, comprising:

• a housing;
• a brushless electric motor drivably connected to an output shaft to impart rotary motion thereto;
• a power supply interface configured to selectively receive a first power supply having a first nominal voltage or a second power supply having a second nominal voltage, wherein the first nominal voltage is greater than the second nominal voltage;
• a switching arrangement having a plurality of motor switches and interposed between the electric motor and the power supply interface;
• and
• a controller configured to control a switching operation of the plurality of motor switches for driving the electric motor, the controller configured to detect a measure of current passing from the power supply to the switching arrangement, compare the measure of current to a current limit, and take corrective action to reduce current delivered to the electric motor if the measure of current reaches or exceeds the current limit,
• wherein the controller is further configured to receive a signal indicative of the first nominal voltage when the first power supply is coupled to the power supply interface and indicative of the second nominal voltage when the second power supply is coupled to the power supply interface, the controller is setting the current limit to a first current limit value when the signal is indicative of the first nominal voltage and to a second current limit value when the signal is indicative of the second nominal voltage, wherein the first current limit value is smaller than the second current limit value by an amount corresponding to a different between the first nominal voltage and the second nominal voltage so as to obtain an output power of the power tool that is substantially the same for the first power supply and the second power supply, wherein the first nominal voltage is approximately twice the second nominal voltage and the first current limit value is approximately half the second current limit value.

A power tool, comprising:

• a housing;
• a brushless electric motor drivably connected to an output shaft to impart rotary motion thereto;
• a power supply interface configured to selectively receive a first power supply having a first nominal voltage or a second power supply having a second nominal voltage, wherein the first nominal voltage is greater than the second nominal voltage;
• a switching arrangement having a plurality of motor switches and interposed between the electric motor and the power supply interface;
• and
• a controller configured to control a switching operation of the plurality of motor switches for driving the electric motor, the controller configured to detect a measure of current passing from the power supply to the switching arrangement, compare the measure of current to a current limit, and take corrective action to reduce current delivered to the electric motor if the measure of current reaches or exceeds the current limit,
• wherein the controller is further configured to receive a signal indicative of the first nominal voltage when the first power supply is coupled to the power supply interface and indicative of the second nominal voltage when the second power supply is coupled to the power supply interface, the controller is setting the current limit to a first current limit value when the signal is indicative of the first nominal voltage and to a second current limit value when the signal is indicative of the second nominal voltage, wherein the first current limit value is smaller than the second current limit value by an amount corresponding to a different between the first nominal voltage and the second nominal voltage so as to obtain an output power of the power tool that is substantially the same for the first power supply and the second power supply,
• wherein the controller operates over periodic time intervals to enforce the current limit on the current delivered to the electric motor, wherein the controller is configured to enforce the current limit by receiving a measure of instantaneous current passing to the switching arrangement within a present time interval of the periodic time intervals, comparing the measure of instantaneous current to the current limit, and, in response to the measure of instantaneous current exceeding the current limit, turning off the motor switches for a remainder of the present time interval and thereby interrupting current flowing to the electric motor.